Method and communication system for selecting a transmission mode for transmitting payload data

ABSTRACT

A transmission mode selection for packet-oriented transmission of useful data between a first and a second communication device is provided, where lists of transmission modes for the communication devices are transmitted to a quality-of-service device. The quality-of-service device uses available transmission resources to select one or more transmission modes from the lists such that the quality of service, which is dependent on the selected transmission modes, can be assured by the available transmission resources. The selected transmission modes are transmitted to a connection controller which prompts further selection of a transmission mode from the transmission modes for the communication devices. The useful data are then transmitted between the communication devices using the transmission mode selected by the further selection.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2006/063853, filed Jul. 4, 2006 and claims the benefitthereof. The International Application claims the benefits of Germanapplication No. 102005036298.2 DE filed Aug. 2, 2005, both of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present invention relates to a method and communication system forselecting a transmission mode for transmitting payload data.

BACKGROUND OF INVENTION

In order to transmit payload data in packet-oriented networks, differentparameters relating to the transmission are typically negotiated betweenthe communication partners of a payload data link as part of a signalingexchange. Said parameters are referred to below as transmission modesand specify e.g. a codec used for encoding and decoding the payloaddata.

In this case the transmission modes for the payload data transmissionare negotiated such that a communication can take place between thecommunication partners. For example, mutually compatible codecs orcodecs which are supported by both partners are selected by thecommunication partners. By means of these compatible codecs a payloaddata link can be set up between the communication partners, while at thesame time the choice of codecs used in particular can have an effect onthe quality of the payload data transmission and on the bandwidth usedfor the payload data transmission.

In a packet-oriented network, link sections can make different bandwidthresources available in each case. For example, a packet-oriented voiceconnection of a teleworker to a terminal device in a LAN (Local AreaNetwork) can be routed via a narrowband telephone line of a publictelephone network to a gateway in the LAN and from there forwarded viabroadband to the terminal device. In many communication systems it oftenhappens that if a non-compressing codec is selected a connection cannotbe set up via the narrowband link section since insufficient bandwidthis available for a payload data link encoded using this codec, whereasif a compressing codec is chosen for the payload data link sufficientbandwidth would still have been available.

Often also, a codec which is highly compressing is chosen for thepayload data link and consequently only delivers a reduced payload dataquality, even though the network makes a sufficiently high bandwidthavailable which would have allowed the use of a low-compression codecwith better payload data quality.

The selection of the codecs and other transmission modes for a payloaddata transmission is in this case often made by the endpoints of theconnection and is often configured in these. In this case theconfiguration—e.g. which codecs are used—can be performed on across-network or network-area-specific basis.

The U.S. Pat. No. 6,671,367 B1 discloses a method wherein a prioritizedlist of preferences is transmitted from an originating signalingendpoint to what is termed a Media Gateway Controller, said list beingmodified by the Media Gateway Controller in such a way that elementswhich are not supported by an associated Media Gateway are removed andthis modified list is transmitted to the Media Gateway.

SUMMARY OF INVENTION

The object of the invention is to specify a method for selecting atransmission mode′ for transmitting payload data, which method enablesdynamic and/or static limiting factors of the network to be taken intoaccount during the selection in order thereby to make an improvedselection. A further object of the invention is to specify acommunication system for performing the method.

This object is achieved by a method as well as a communication system asclaimed in the independent claims. Advantageous embodiments anddevelopments of the invention are set forth in the dependent claims.

In the inventive method for selecting a transmission mode′ fortransmitting payload data between a first and a second communicationdevice, in particular a terminal device such as an IP telephone (IP:Internet Protocol), a multimedia application or a so-called soft clientwith telephony functions on a computer, over a packet-orientedcommunication network, a first list of transmission modes of the firstcommunication device and a second list of transmission modes of thesecond communication device are transmitted, in particular in the courseof a connection setup, to a quality-of-service device. A quality ofservice of the transmission is dependent here on the respectivetransmission mode. A transmission mode can be determined in particularby a codec type, a number of payload data sample values or payload datasegments per payload data packet, the type and/or presence ofencryption, an IP standard used (at the time of the patent application,IP Version 4 or IP Version 6), a size of payload data packets, and/or anumber of payload data packets per time unit. Based on availabletransmission resources of the communication network, thequality-of-service device selects one or more transmission modes fromthe first and second lists such that the quality of service dependent onthe selected transmission modes can be guaranteed by the availabletransmission resources. In addition, the quality-of-service devicetransmits the selected transmission modes to a data link control. Thedata link control, in particular a network node or an active switchingcomponent in the signaling path, a gateway, a gatekeeper or even thefirst or second communication device, initiates a further selection of atransmission mode′ from the transmitted transmission modes for thecommunication devices. The transmission of the payload data, inparticular via a direct payload data link, between the communicationdevices is performed using the transmission mode′ selected by means ofthe further selection.

In this context, what is understood by available transmission resourcescan be in particular a bandwidth upper limit of link sections of thepayload data link, a current capacity utilization of link sections, astatistical or historical capacity utilization of link sections takinginto consideration the network based on topology information. Topologyinformation is understood to mean in particular the structure of thenetwork and maximum bandwidths or capacity upper limits of respectivelink sections. Topology information can also, for example, specifylimiting the number of voice connections that can be conducted inparallel over a narrowband subscriber line to a small value such as oneor two, or setting an upper limit for a multimedia application to 128kbit/s in order to allow other data transmissions on the network inaddition to the voice connections.

The inventive communication system for selecting a transmission mode′for transmitting payload data between a first and a second communicationdevice over a packet-oriented communication network, wherein a qualityof service of the transmission is dependent on the respectivetransmission mode, includes a quality-of-service device for receiving afirst list of transmission modes of the first communication device and asecond list of transmission modes of the second communication device.Also provided is the quality-of-service device for selecting one or moretransmission modes from the first and second lists, with the selectionbeing made on the basis of available transmission resources of thecommunication network such that the quality of service dependent on theselected transmission modes can be guaranteed by the availabletransmission resources. Furthermore, the quality-of-service device isprovided for transmitting the selected transmission modes to a data linkcontrol. The inventive communication system additionally includes thedata link control for initiating a further selection of a transmissionmode′ from the transmission modes transmitted by the quality-of-servicedevice for the communication devices, and a transmission device fortransmitting the payload data between the communication devices usingthe transmission mode′ selected by means of the further selection.

The invention is advantageous insofar as the quality-of-service devicecan take into account comprehensive static and dynamic information ofthe network during the selection of the transmission modes, whichinformation is usually not available to the first or secondcommunication device. This permits a better selection of thetransmission modes that is matched to actual conditions. It also provesadvantageous that an otherwise customary configuration of thecommunication devices with regard to selection of the transmission modesis made easier or can even be dispensed with. This results in increasedflexibility and simplifies the administration of the network. A furtheradvantage is the enabling of a bandwidth-optimized payload datatransmission, which is characterized in that a use of bandwidthresources can be optimized, taking into account a requirement in termsof the quality of the payload data and/or the payload data transmissionand taking into account resource upper limits.

It is also advantageous that the topology of the network can be takeninto consideration during the selection of the transmission modes andhence the transmission resources of link sections of the network can betaken into account. In this case it is possible to map the topology ofthe network in a different granularity and—depending onrequirements—administer link sections separately or in groups andevaluate them within the scope of the invention. Thus, for example,subnetworks of the network can be considered by the quality-of-servicedevice as a single entity with the same transmission resources.

It is also advantageous that an overdimensioning of the network due tothe provisioning of disproportionately large transmission resources canbe dispensed with. Alternatively and/or in addition, thequality-of-service device enables the utilization of the network'scapacity to be optimized.

The subdivision of the selection of the transmission modes into apreselection by the quality-of-service device and a subsequent finalselection initiated by the data link control is advantageous insofar as,for example, the quality-of-service device only evaluatescross-subnetwork topology information during the preselection, whereassubnetwork-internal criteria are evaluated in the final selection. Thistwo-stage process reduces in particular the complexity of the evaluationof the selection of the transmission modes.

Furthermore, in an advantageous development of the invention it is evenpossible to apply a three-stage method wherein the quality-of-servicedevice carries out a preselection of the transmission modes, the datalink control itself makes a subsequent selection of the transmissionmodes, and yet the final selection of the transmission modes, initiatedby the data link control, is performed by the communication devices.

In an advantageous development of the invention it is possible, duringthe selection of the transmission modes by the quality-of-servicedevice, to perform a transmission-mode-specific quality-of-servicecomparison and/or bandwidth comparison, the bandwidth comparisonrepresenting a comparison of a required bandwidth with an availablebandwidth. Analogously, the quality-of-service comparison represents acomparison of a desired quality of service with an available quality ofservice. Based on the selection of the transmission modes, aquality-of-service/bandwidth reservation can be made.

A bandwidth comparison or test of this kind can determine in particulara currently available maximum bandwidth and compare this with a minimumrequired bandwidth resulting according to the possible transmissionmode, contained in the first and second lists. This is advantageous tothe extent that bandwidth reservations made for already establishedconnections can be stored in the quality-of-service device and hence beused in a following evaluation and selection of transmission modes.

The bandwidth reservation can be made for one of the transmission modesselected by the quality-of-service device, preferably what is termed a“worst case” method being applied to reserve that bandwidth whichrequires the highest bandwidth out of the entries. In this case thebandwidth reservation can be performed separately for individual linksections.

Preferably the selection of the transmission modes and the bandwidthreservation can be performed by the quality-of-service device in asingle transaction in order thereby to avoid overlaps with contendingreservations in the time window between transmission mode selection andreservation. In this case the data link control addresses a singlerequest to the quality-of-service device containing all the relevantinformation about the transmission modes of the two communicationdevices. The quality-of-service device responds with the list ofselected transmission modes.

In a development of the invention, the transmission mode selected duringthe further selection can be communicated to the quality-of-servicedevice. Preferably this happens following final selection of thetransmission mode′ and before an end-to-end setup of the payload datatransmission. Depending on the selected transmission mode, thequality-of-service device can perform a bandwidth reservation or updatea previously completed bandwidth reservation. This is advantageous tothe extent that in this way the precisely used bandwidths are now madeknown to the quality-of-service device and these values can be used forevaluations of succeeding method sequences for further payload datalinks.

Preferably a bandwidth of the payload data link can also be set upaccording to the reserved bandwidth during the setup of a payload datalink for transmission of the payload data. In addition, upon terminationof the payload data link, the bandwidths set up and the bandwidthsreserved in the quality-of-service device can be released again. Thelatter can preferably take place as a result of a notification messagefrom one of the communication devices or the data link control to thequality-of-service device.

In an advantageous embodiment of the invention, the quality-of-servicedevice can select the one transmission mode or the plurality oftransmission modes from the first and second lists such that bothcommunication partners support the transmission modes.

In a further advantageous embodiment of the invention, the transmissionmodes of a bi-directional connection can be determined and selectedseparately for each transmission direction.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is explained below withreference to the drawing, in which:

FIGS. 1-2 show in a schematic representation a communication system withtwo IP telephones connected to each other via data link controls and

FIG. 3 schematically illustrates transmitted transmission modes andtransmission resources of a subnetwork of the communication system.

DETAILED DESCRIPTION OF INVENTION

FIGS. 1-2 show in a schematic representation a communication system withtwo IP telephones EG1, EG2 as first (EG1) and second (EG2) communicationdevices, three data link controls VS1, VS2, VS3, and aquality-of-service device DGE. All these cited components cancommunicate with one another via an IP network IPN, as indicated bymeans of dashed lines between these components. In this scheme let thefirst IP telephone EG1 be assigned to the first data link control VS1,and the second IP telephone EG2 to the second data link control VS2,these assignments being represented by an unbroken line between therespective components and e.g. having been set up by means of a priorconfiguration of the data link controls VS1, VS2 and/or the IPtelephones EG1, EG2.

Signaling links SIG1, SIG2, SIG3, SIGD1, SIGD2, SIG12 are represented assingle continuous double arrow lines, while a payload data link NV isrepresented as a double continuous double arrow line. In the presentexemplary embodiment, let payload data be voice data between the two IPtelephones EG1, EG2. A path of the payload data link from the first IPtelephone EG1 to a first router R1 via the first path section NV1, via asecond path section NV2 to a second router R2 and from there via a thirdpath section NV3 to the second IP telephone EG2 is represented by meansof a dotted line. In this case let payload data traffic be routed viathe two routers R1, R2, without the two routers R1, R2 encoding and/ordecoding the payload data. Let it be assumed that the payload data isencoded and/or decoded solely in the two IP telephones EG1, EG2. Aconnection of this kind is usually referred to as a direct payload datalink or direct payload between the communication devices.

Real-time requirements need to be taken into account for thetransmission of the voice data, e.g. in accordance with the IP telephonytechnologies H.323 and SIP (Session Initiation Protocol). The so-calledReal-Time Transport Protocol (RTP) is often used as the protocol fortransmitting the voice data, serving in particular to transportmultimedia data streams (audio, video, text, etc.) over packet-orientednetworks. The payload data is encoded for transport—often in a lossymanner due to compression of the payload data—and transmitted in datapackets.

FIG. 1 schematically shows a connection setup for a transmission ofpayload data with real-time requirements, wherein a selection of atransmission mode′ for the two IP telephones EG1, EG2 is made by thequality-of-service device DGE.

The first IP telephone EG1 initiates a call to the second IP telephoneEG2. In the course of a thereby beginning connection setup signaling,the supported transmission modes of the first IP telephone EG1 aretransmitted to the second data link control VS2 in the signaling linkSIG1. In the present exemplary embodiment let the transmission modes bespecified by the supported codecs of the first IP telephone EG1,parameters for the voice sample values per payload data packet and thetype of encryption of the payload data. The second data link control VS2now interrupts the further signaling to the second IP telephone EG2 insuch a way that in this method step the signaling to the second IPtelephone EG2 is held back and no message relating to the call setup istransmitted to the second IP telephone EG2 or only a message istransmitted without the supported transmission modes of the first IPtelephone EG1.

The second data link control VS2 also generates a first list of thetransmission modes supported by the first IP telephone EG1. In addition,the second data link control VS2 generates a second list of thetransmission modes supported by the second IP telephone EG2, saidlast-mentioned transmission modes of the second data link control VS2having been made known on account of a registration of the second IPtelephone EG2 with the second data link control VS2 or having beenqueried by means of message traffic in the course of the previous orcurrent connection setup.

The second data link control VS2 now deletes from the two lists thosetransmission modes which are not supported by the communication partnersand which at selection time would therefore not allow a successfulpayload data transmission and would consequently not be selected by thequality-of-service device DGE in any case.

Considered generally, in an alternative embodiment a single list can begenerated in this step from the transmission modes supported by the twoIP telephones EG1, EG2, with only this one list needing to be handled inthe further course of the connection.

The two lists, possibly after the aforesaid modification of the lists,are now transmitted to the quality-of-service device DGE within thesignaling link SIG2.

In FIG. 1, the quality-of-service device DGE is embodied as a serverwhich, with the aid of topology and capacity utilization information,selects one or more transmission modes from the first and second listssuch that predefined or predefinable criteria are satisfied. Onecriterion here is that a direct payload data transmission is madepossible between the first (EG1) and second IP telephone EG2. A secondcriterion is that a predefined transmission resource, e.g. a bandwidthon a link section of the payload data link, is not exceeded. Theselection of codecs and packet rates for the payload data transmissionalso has an impact on the available transmission resources. A thirdcriterion here can be that a quality of service including the voicequality and a voice delay can be guaranteed. A fourth criterion can berestrictive information relating to link sections which, for example,prevent the transmission of data according to a certain protocol on therespective link section.

To evaluate said criteria, the quality-of-service device DGE can accesstopology information concerning the structure of the IP network IPN andconcerning current and statistical capacity utilization informationrelating to link sections within this IP network IPN. This informationcan be stored in a database, in which case the data in the database canbe configured—e.g. via XML configuration files (XML: Extensible MarkupLanguage)—, can be queried by a further server, or can be ascertained bymeans of test messages.

On the basis of the first and second lists and available transmissionresources of the IP network IPN, the quality-of-service device DGE nowselects one or more transmission modes from the first and second listssuch that the quality of service dependent on the selected transmissionmodes can be guaranteed by the available transmission resources.According to the embodiment of the quality-of-service device DGE, thelatter now returns a common list for the two lists or a modified listfor each of the two lists to the second data link control VS2 via thesignaling link SIG2.

In a special case (not shown) the lists created by thequality-of-service device DGE are empty and no transmission modes can beselected. No communication is possible between the IP telephones EG1,EG2. This is communicated in subsequent method steps to the IPtelephones EG1, EG2 by means of signaling messages. This can usually beomitted for the second IP telephone EG2, because the latter has notinitiated a connection setup.

In a further case to be considered in particular, only a singletransmission mode per transmission direction is transmitted to thesecond data link control VS2. This can be the case in particular whenonly one transmission mode could be found or if the quality-of-servicedevice DGE has been instructed to return, per transmission direction,only that transmission mode which can best satisfy the examinedcriteria. This selected transmission mode is then transmitted to the twoIP telephones EG1, EG2 via the signaling links SIG1 and SIG3, whereupona payload data link NV can be set up using the selected transmissionmodes.

In a more general description, the quality-of-service device DGE cantransmit two restricted lists, each containing at least one entry, tothe second data link control VS2. The latter can now make a furtherselection in the lists based on further criteria and thereby furtherrestrict the lists or process the lists further in unmodified form.

Subsequently, the connection setup message held back up to this methodstep is forwarded by the second data link control VS2 to the second IPtelephone EG2 in the course of the signaling SIG3, the contents of thesecond, restricted list being included in the signaling message. A listof permitted codecs or codecs preferred for selection is thustransmitted to the second IP telephone EG2.

By means of this modified signaling SIG3, the second data link controlVS2 causes the called, second IP telephone EG2 to make a selection ofprecisely one transmission mode′ per transmission direction from themodified second list. Similarly, the second data link control VS2effects the transmission of the restricted first list to the first IPtelephone EG1 in the course of the signaling SIG1 and causes saidcalling, first IP telephone EG1 to select precisely one transmissionmode′ from the first list.

In this case the two IP telephones EG1, EG2 select the transmission modeon the basis of configured rules. Following the selection of thetransmission modes in the two IP telephones EG1, EG2, the payload datalink NV can be set up between the first IP telephone EG1 and the secondIP telephone EG2, with the selected transmission modes being used by thetwo IP telephones EG1, EG2 as inventive transmission devices during theencoding/decoding and the sending/receiving of the payload data. Inparticular, a selected codec is used for encoding and/or decoding, thepackets are sent and/or received at a selected data packet rate, and thepackets are encrypted using the selected type of encryption.

In the exemplary embodiment, a direct payload data link NV—routed viathe routers R1 and R2—is thus enabled between the two IP telephones EG1,EG2, while at the same time a quality of service of the voicetransmission dependent on the respective transmission mode can beoptimized such that topology information and capacity utilizationinformation are taken into account.

Considered generally, the quality-of-service device DGE can be arule-based system during the processing of the two lists or process thecriteria on the basis of specifications or rules, referred to aspolicies. These are, for example, restrictions per link section, perpayload data type to be transmitted (voice, multimedia, etc.) or perdefined or specified capacity utilization threshold values.

The restricted lists which the quality-of-service device DGE transmitsto the second data link control VS2 can include priorities for thesubsequent final selection of the transmission modes. In this case theindividual list elements can be assigned priority levels or the order ofthe elements in the list reflects a priority of the elements. In thisway it can be communicated to the second data link control VS2 which ofthe transmission modes are to be selected by preference based on thecheck by the quality-of-service device DGE.

Advantageously, the quality-of-service device DGE also includes afunctionality for querying the currently available transmissionresources, in particular the bandwidths, in the IP network IPN. Thisenables the selection of the transmission modes to be based on thecurrent capacity utilization of the IP network IPN. A bandwidthreservation can also be made by the quality-of-service device DGE, whichreservation can then be taken into account during the selection of thetransmission modes, since a required bandwidth for the payload data canbe determined for an examined transmission mode and compared with thebandwidth that is available. In this case the bandwidth reservation canbe based on a worst-case approach, wherein following the selection of aplurality of transmission modes that bandwidth is reserved for therestricted first and second lists which is the largest out of all thetransmission modes in the lists. In the final selection of thetransmission modes in the second data link control VS2 or in the two IPtelephones EG1, EG2, this bandwidth reservation can then be updated inaccordance with the bandwidth actually used. Furthermore, what isreferred to as a release request can be transmitted to thequality-of-service device DGE following termination of the call, inorder to release the reserved bandwidth.

The method presented thus far in a protocol-neutral manner will beexplained once again below with reference to a use of H.323 or SIP forthe signaling. Thus, in the case of H.323, for example, what is termedthe SETUP message can be used within the signaling link SIG1 for thetransmission of the transmission modes supported by the first IPtelephone EG1, the transmission modes being transmitted in an H.245Container message. The transmission modes of the called, second IPtelephone EG2 can either be requested from the second IP telephone EG2by the second data link control VS2 by means of a proprietary message,be configured in the second data link control VS2, or be taken from apreceding H.323 signaling message.

Upon arrival of the SETUP message at the second data link control VS2,said message is temporarily detained in the second data link control VS2and the transmission modes contained therein are extracted from themessage and transmitted to the quality-of-service device DGE. Afterreception of a response from the quality-of-service device DGE as partof the signaling SIG2 with the modified first and second lists, theSETUP message is modified by the second data link control VS2 in such away that only the transmission modes satisfying the criteria remaincontained in the SETUP message. This modified SETUP message is thentransmitted to the called, second IP telephone EG2. All further stepsfor the connection setup are then continued in accordance with standardconnection setup methods.

When SIP is used for the signaling, what is termed an INVITE message istransmitted by the calling, first IP telephone EG1 to the second datalink control VS2, the transmission modes supported by the first IPtelephone EG1 being transmitted in an SDP Container message (SDP:Session Description Protocol). The second data link control VS2 canquery the called, second IP telephone EG2 for its supported transmissionmodes by means of what is termed an OPTIONS request, the transmissionmodes can be configured in the second data link control VS2, or they canbe taken from the so-called SIP Precondition Handling in accordance withRFC3312. The further method steps are then analogous to H.323, i.e. theINVITE message is held back and the transmission modes contained thereinare transmitted with modifications, determined by the quality-of-servicedevice DGE, to the called, second IP telephone EG2.

FIG. 2 schematically depicts method steps in a communication system inwhich the two IP telephones EG1, EG2 directly transmit the lists oftheir supported transmission modes to the quality-of-service controllerDGE. In this case let the inventive data link control be part of thefirst and/or second IP telephone EG1, EG2. When a voice connection isinitiated, the first IP telephone EG1 transmits a message SIGD1containing its supported transmission modes and an identifier of thefirst IP telephone EG1 to the quality-of-service device DGE. Theidentifier permits a unique identification of the first IP telephone EG1and can be e.g. the IP address of the first IP telephone EG1. In thefurther course of the signaling, the second IP telephone EG2 uses thesignaling message SIGD2 to send its own list of transmission modes andthe identifier of the first IP telephone EG1 to the quality-of-servicecontroller DGE which, on the basis of the identifier, performs theassignment of the two IP telephones EG1, EG2 that are to be connected.

Analogously to the previously described method steps, thequality-of-service device DGE now determines a restricted selection oftransmission modes and transmits this to the second IP telephone EG2.The latter now selects a transmission mode therefrom and transmits thiswithin the signaling link SIG12 to the first IP telephone EG1.Alternatively, the transmission mode can be selected exclusively via thesignaling link SIGD2. In this case the second IP telephone EG2 receivesthe list from the first IP telephone EG1 and can contact thequality-of-service device, at the same time contributing its own list.

FIG. 3 illustrates the transmitted transmission modes and thetransmission resources of a subnetwork with the aid of the signalingSIG1, SIG2, SIG3 according to FIG. 1. A list of transmission modes shownin FIGS. 3 a, 3 b, 3 c and 3 e is in this case represented by means of arectangle subdivided into sections. The topology of a subnetwork for thepayload data link between the first IP telephone EG1 and the second IPtelephone EG2 via the routers R1 and R2 is represented by means ofrectangles for the IP telephones EG1, EG2 and for the routers R1, R2, aswell as by means of unbroken lines for link sections V1, V2, V3 betweenthe IP telephones EG1, EG2 and routers R1, R2 (FIG. 3 d). The availabletransmission resources for each of the link sections are shown in FIG. 3d as comma-separated lists. Only codecs are considered as transmissionmodes in FIG. 3. Other transmission modes are handled in a similarmanner, but for reasons of clarity are not shown. Furthermore, theexample relates only to the transmission direction from the first IPtelephone EG1 to the second IP telephone EG2. The opposite direction isto be regarded analogously and is therefore not described.

FIG. 3 a shows the first list of codecs supported by the first IPtelephone EG1, which list is transmitted to the second data link controlVS2 within the signaling link SIG1. Let the supported codecs of thefirst IP telephone EG1 be the codecs G.711, G.722, G.723.1, G.729,G.729AB.

FIG. 3 b shows the second list of codecs supported by the second IPtelephone EG2, which list is transmitted to the second data link controlVS2 within the signaling link SIG3, or the codecs are known owing to aregistration or configuration. Let the supported codecs of the second IPtelephone EG2 be the codecs G.711, G.722, G.726, G.729, G.729AB.

The second data link control now transmits these two lists to thequality-of-service device DGE within the signaling link SIG2. The twotransmitted lists are shown in FIG. 3 c and include the aforementionedcodecs.

The quality-of-service device DGE now makes a selection of thetransmission modes by evaluating topology information of the network andtaking into account bandwidth and codec parameters for the link sectionsV1, V2, V3. The topology to be evaluated and the parameters are shown inFIG. 3 d. It is shown here that the payload data link NV to be set up isrouted from the first IP telephone EG1 via the link section V1 to therouter R1, from the router R1 via the link section V2 to the router R2,and from the router R2 via the link section V3 to the second IPtelephone EG2. Based on a current capacity utilization of the linksections and based on topology restrictions—e.g. the link section V1could be a narrowband telephone subscriber line and the link section V2a broadband LAN connection, with, though, already assigned transmissionresources for simultaneously active connections needing to be taken intoaccount in each case—the quality-of-service device DGE establishes thata connection setup using the codecs G.723.1 and G.729 is possible viathe link section V1, a connection setup using the codecs G.711, G.722,G.728 and G.729 is possible via the link section V2, and a connectionsetup using the codecs G.711, G.722 G.729 and G.726 is possible via thelink section V3. In order to perform the transmission of the payloaddata over all three link sections V1, V2, V3, the quality-of-servicedevice DGE recognizes that for voice encoding only the codec G.729supports an end-to-end connection. The quality-of-service device DGEthereupon modifies the two lists in such a way that a common list ofcodecs supported jointly by the two IP telephones EG1, EG2 is createdwhich only contains the codec G.729. This common, restricted list—shownin FIG. 3 e—which contains a selection from the first and second lists,is now transmitted via the signaling link SIG2 to the second data linkcontrol VS2 and thus includes only codecs which are supported by both IPtelephones EG1, EG2.

With the selected codec G. 729 , the second data link control VS2 cannow initiate the payload data transmission NV for the voice connection.

Further embodiments of the invention that are not shown can provide thatin order to create the first and/or second list the second data linkcontrol VS2 determines the transmission modes of the first and/or secondcommunication device (EG1, EG2) from a connection setup signaling—forexample the signaling link SIG1—for the transmission of the payloaddata, from a preceding signaling, from a registration of the firstand/or second communication device (EG1, EG2) with the second data linkcontrol VS2, and/or a configuration of the second data link control VS2.The last-mentioned options in particular enable the lists to be sent tothe quality-of-service device DGE to be generated without querying thecommunication device (EG1, EG2) and therefore without delay.

In a further embodiment of the invention that is not shown, the payloaddata can be transmitted in a media stream, in which case thetransmission modes that are incompatible with the media stream can beomitted from the lists to be transmitted to the quality-of-servicedevice.

As an alternative to the previously explained exemplary embodiment, themethod sequence can also be modified such that, provided—as in thepresent exemplary embodiment—the second communication device is aterminal device, the first communication device transmits the first listof transmission modes to the data link control by means of a signalingmessage intended for the second communication device, the data linkcontrol stores the first list and transmits the signaling message to thesecond communication device, and the second communication devicesuppresses a visual and/or acoustic signaling, e.g. in the form of aringtone, that is usual as part of a connection setup. The data linkcontrol can also transmit the first and second lists to thequality-of-service device and, after receiving the selected transmissionmodes from the quality-of-service device, the data link control canagain transmit a signaling message to the second communication device,in which case only the transmission modes selected by thequality-of-service device or parts of the selected transmission modescan be contained in the signaling message. In this case the reception ofthis signaling message can cause the second communication device tooutput the visual and/or acoustic signaling.

In a further alternative method sequence, the first communication devicetransmits the first list of transmission modes to the data link controlby means of a signaling message intended for the second communicationdevice and the data link control forwards the signaling message to thesecond communication device. In addition, the second communicationdevice transmits the second list of transmission modes to the data linkcontrol in a response message, whereupon the data link control transmitsthe first and second lists to the quality-of-service device. Later,after receiving the transmission modes selected by thequality-of-service device, the data link control transmits to the firstand second communication device a further signaling message containingin each case the transmission modes selected by the quality-of-servicedevice or parts of the selected transmission modes.

The method steps presented can be used in particular with networkprotocols QSIG (signaling at the Q reference point) via SIP, QSIG viaH.323 (Annex M.1), with H.323 (Annex M.1) defining the tunneling ofsignaling protocols via H.323, for the overall connection or for thepartial connections of transit sections. Furthermore, the method can beused with ISUP (ISDN User Part) via SIP, ISUP via H.323, DSS1 (DigitalSubscriber Signalling System No. 1) via SIP, DSS1 via H.323, as well asfor H.323 for IP Centrex solutions.

1.-10. (canceled)
 11. A method for selecting a transmission mode fortransmitting payload data between a first and a second communicationdevice over a packet-oriented communication network, wherein aquality-of-service of the transmission is dependent on the respectivetransmission mode, the method comprising: transmitting a first list anda second list to a quality-of-service device, the first list oftransmission modes supported by the first communication device, and thesecond list of transmission modes supported by the second communicationdevice, the second list generated independently of the first list;selecting at least one transmission mode from the first and second listsby the quality-of-service device, the selection based on availabletransmission resources of the communication network such that thequality of service dependent on the selected transmission mode isguaranteed by the available transmission resources; transmitting theselected transmission mode from the quality-of-service device to a datalink control; initiating a further selection of a transmission mode bythe data link control, the further selection based on the selectedtransmission mode transmitted to the data link control; and transmittingthe payload data between the communication devices using thetransmission mode selected in the further selection.
 12. The method asclaimed in claim 11, wherein the transmission mode selected by thequality-of-service device is supported by both communication devices.13. The method as claimed in claim 11, wherein a preselection is madefor the lists to be transmitted such the lists include only transmissionmodes that are supported by both communication devices and that thefirst and second lists are created from the preselected transmissionmodes.
 14. The method as claimed in claim 11, wherein to create at leastone of the lists, the transmission modes of the respective communicationdevice are determined from at least once condition selected from thegroup consisting of: a connection setup signaling for the transmissionof the payload data, a preceding signaling, a registration of therespective device with the data link control, and a configuration of thedata link control.
 15. The method as claimed in claim 11, wherein when aplurality of transmission modes are selected by the quality-of-servicedevice, each selected mode is assigned a different priority level,thereby providing a recommendation for the further selection.
 16. Themethod as claimed in claim 11, wherein during the selection of thetransmission mode by the quality-of-service device: atransmission-mode-specific comparison of a required bandwidth with anavailable bandwidth is performed, and a bandwidth reservation is madebased on the selection.
 17. The method as claimed in claim 16, whereinthe comparison of a required bandwidth with an available bandwidth isperformed as part of a call acceptance check.
 18. The method as claimedin claim 11, further comprising: transmitting the further selectedtransmission mode to the quality-of-service device, and requesting, bythe quality-of-service device, a bandwidth reservation in accordancewith the further selected transmission mode.
 19. The method as claimedin claim 11, further comprising: transmitting the further selectedtransmission mode to the quality-of-service device, and updating, by thequality-of-service device, a previous bandwidth reservation inaccordance with the further selected transmission mode.
 20. The methodas claimed in claim 11, wherein the first communication device transmitsthe first list of transmission modes to the data link control via asignaling message intended for the second communication device, whereinthe data link control delays forwarding the signaling message andtransmits the first and second list to the quality-of-service device,wherein after receiving the transmission mode selected by thequality-of-service device, the data link control modifies the delayedsignaling message such the transmission modes of the signaling messageare replaced by at least a portion of the transmission mode selected bythe quality-of-service device, and wherein the modified signalingmessage is transmitted to the second communication device.
 21. Acommunication system for selecting a transmission mode for transmittingpayload data between a first and a second communication device over apacket-oriented communication network, wherein a quality of service ofthe transmission is dependent on the respective transmission mode,comprising: a quality-of-service device for: receiving a first list oftransmission modes supported by the first communication device,receiving a second list of transmission modes supported by the secondcommunication device, the second list generated independently of thefirst list, selecting one or more transmission modes from the first andsecond lists on the basis of available transmission resources of thecommunication network such that the quality of service dependent on theselected transmission modes is guaranteed by the available transmissionresources, and transmitting the selected transmission modes to a datalink control; the data link control for initiating a further selectionof a transmission mode from the transmission modes transmitted by thequality-of-service device for the communication devices; and atransmission device for transmitting the payload data between thecommunication devices using the transmission mode selected via thefurther selection.